Due to a recent trend toward high integration in semiconductor memory devices and CMOS image sensors, geometric structures in these semiconductor devices and components therein have necessarily changed.
FIG. 1 is a cross sectional view of a prior art thin film transistor. As shown in FIG. 1, a prior art semiconductor device includes an active region AR and a field region FR in a silicon semiconductor substrate 1. A device isolation layer 2 is formed in the field region FR.
The device isolation layer 2 may be formed in an LOCOS process by forming an oxidation-resistant insulating layer in the field region FR, and by selectively performing a thermal-oxidation process on the oxidation-resistant insulating layer. Alternatively, the device isolation layer 2 may be formed in a sequential process of forming an oxidation-resistant insulating layer in the active region AR, forming a trench by selectively removing the semiconductor substrate in the field region FR, forming an oxide layer to fill the trench, and selectively removing the oxide layer to expose the surface of the semiconductor substrate by a CMP process, wherein the device isolation layer 2 is formed in the trench.
Next, the semiconductor device, for example, the thin film transistor 10, is formed in the active region AR. That is, the thin film transistor 10 is formed with a gate insulating layer 11 and a gate electrode 12, by sequentially depositing and selectively removing portions of the gate insulating layer 11 and a conductive layer on the semiconductor substrate 1.
Subsequently, an insulating layer is deposited on the entire surface of the semiconductor substrate 1. This insulating layer is anisotropically etched to form sidewall-insulating layers 13 on opposite sidewalls of the gate electrode 12. Next, impurity ions are implanted into the active region AR of the semiconductor substrate 1 on opposite sides of the gate electrode 12 while using the gate electrode 12 and the sidewall-insulating layers 13 as a mask to thereby form source/drain regions 14.
Next, a metal line (not shown) is formed on the semiconductor substrate 1. A silicide layer 15 is then formed on the surfaces of the source/drain regions 14 to enhance the electric contact with the source/drain regions 14.
In the above described thin film transistor structure, the silicide layer 15 is formed in a sequential process of depositing a refractory metal on the entire surface of the semiconductor substrate 1, and then performing a thermal process thereon. As a result, the silicide layer 15 is formed on the surface of the source/drain regions 14 at an interface between the silicon semiconductor substrate 1 and the refractory metal. If the gate electrode 12 is formed of silicon, the silicide layer 15 is also formed on the surface of the gate electrode 12.
However, when the thermal process is performed on the refractory metal on the entire surface of the semiconductor substrate 1 to form the silicide layer 15 on the surface of the source/drain regions 14, a silicide layer 15a is also formed in the interfaces between the device isolation layers 2 and the source/drain regions 14. That is, ions of the refractory metal penetrate into the interfaces between the device isolation layers 2 and the source/drain regions 14. As a result, silicide layers 15a are formed in the interfaces between the device isolation layers 2 and the source/drain regions 14.
The device isolation layer 2 and the source/drain regions 14 are formed of different materials, at different thickness, and in different surface states. Therefore, it is difficult to maintain a uniform thickness of the silicide layers 15a formed in the interfaces between the device isolation layers 2 and the source/drain regions 14 without an additional process. Furthermore, the silicide layers 15a formed in the interfaces between the device isolation layers 2 and the source/drain regions 14 may cause a leakage current, thereby deteriorating the quality of the resulting semiconductor device.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.